In this fourth book of Meddaugh's Martha series, the mild-mannered pooch who derives the power of speech from alphabet soup takes herself for a stroll. When someone calls her a ""good dog,"" she ingenuously replies, ""What other kind of dog is there?"" She soon has her answer when she meets Bob, a hulking, bearlike mutt who viciously barks at passers-by. Bob's bearded owner is ""just as ferocious,"" berating his pet with the words, ""Bad dog Bob! Bad dog!"" She moves on to another neighbor's yard, where she teaches a parrot to call her a ""good dog."" Martha's big mouth gets her into trouble when she returns to lecture Bob, not realizing that he has broken free of his thick metal chain. Fortunately, he chases Martha into the parrot's yard, where the magic words--""good dog!""--save Martha from certain doom. As in previous volumes, Meddaugh carries much of the story forward through dialogue that appears in hand-lettered voice bubbles, and her illustrations winningly convey the characters' personalities. The golden-brown, thick-waisted heroine's deep sincerity, with her drooping ears and expressive eyes, balance her comical self-righteous streak. The lunging, growling Bob is genuinely scary, but compliments tame his anger and smooth his shaggy coat. Young animal lovers should be warned that not every snarling bad dog can be as miraculously transformed as Bob into an earnest good dog. Nevertheless, Meddaugh successfully sends the message that pets (and their owners) respond best to kindness. Ages 4-8. (Oct.)